Reflex liquid crystal display device, display apparatus, projection optical system, and projection display system

ABSTRACT

A superior reflex type vertically-aligned liquid crystal display device wherein the refractive index anisotropy Δn of its liquid crystal material is controlled to be more than 0.1, and the transmissivity of the liquid crystal is saturated with facility at a low voltage below 5 to 6V despite a reduction of the thickness of the vertically-aligned liquid crystal layer to less than 2 μm, hence achieving satisfactory driving at a practically low voltage while attaining another advantage of remarkable improvement in the transmissivity itself. Therefore, the display device indicates a sufficient transmissivity, an excellent low-voltage driving characteristic and a fast response. Further improvements are realizable in a display apparatus, a projection optical system and a projection display system by the use of such display device.

TECHNICAL FIELD

[0001] The present invention relates to a reflex liquid crystal(electro-optical) display device adapted for a projection display systemor the like, and also to a display apparatus, a projection opticalsystem and a projection display system used in combination with such adisplay device.

BACKGROUND ART

[0002] With the recent progress in realizing improved projection displaywith a high definition, a small size and a high luminance, there arenoted and practically utilized reflex display devices which are suitedfor achieving a dimensional reduction with an enhanced definition andare capable attaining a high optical efficiency.

[0003] Out of such display devices, there is reported an active reflexliquid crystal display device wherein a driving element is provided on asilicon substrate which is positioned opposite to a glass substratehaving a transparent electrode formed therein and is composed of, e.g.,a CMOS (complementary metal oxide semiconductor) circuit, and a drivingcircuit substrate having an aluminum optical reflecting electrode isplaced thereon, and a vertically-aligned liquid crystal material isinjected between the pair of such substrates (Paper (1): H. Kurogane etal., Digests of SID1998, p. 33-36 (1998); Paper (2): S. Uchiyama et al.,Proceedings of IDW2000, p. 1183-1184 (2000)). The devices of this typehave practically been commercialized by some makers.

[0004] Here, the vertically-aligned liquid crystal material is onehaving a negative permittivity anisotropy (i.e., Δε (=ε(∥)−ε(⊥), whichis the difference between the parallel permittivity ε(∥) and thevertical permittivity ε(⊥) to the major axis of the liquid crystalmolecule, is negative). When the voltage applied between its transparentelectrode and light reflecting electrode is zero, the liquid crystalmolecules are oriented to be substantially vertical to the substrateplane to thereby give display in a normally black mode.

[0005] The thickness (cell gap) of the vertically-aligned liquid crystallayer in the conventional reflex device reported in the above theses is3 to 4 μm, and the curve of the liquid crystal transmissivity to thedriving voltage applied to the liquid crystal (hereinafter referred toas V-T curve, which corresponds to the reflectivity of the devicemeasured actually in the reflex device; it is supposed here that theincident light, e.g., s-polarized light, is modulated into p-polarizedreflected light by the device as will be described later) has suchcharacteristic that it rises at a threshold voltage of 2V or so andreaches its maximum value at an applied voltage of 4 to 6V. Thetransmissivity of the liquid crystal is changed analogously by changingthe voltage between the electrodes to thereby realize expression ofgradations. FIG. 14 graphically shows data excerpted as an example fromPaper (1) cited above. According to the reported data, the liquidcrystal layer has a thickness of 3 μm, the driving voltage isapproximately ±4V, and the response speed (rise time+fall time) is 17msec or so.

[0006] Normally the liquid crystal is driven while the voltage isinverted to be positive or negative per frame or field, so that theabove device is actually driven by a voltage of ±4 to 6V at the maximum.(Since the positive and negative V-T curves are mutually symmetrical inprinciple, it is usual that the V-T curve is expressed as positivealone.) It is also defined that a liquid crystal driving voltage of ±4to 6V needs to be more than 8 to 12V as an effective withstand voltageof a driving transistor.

[0007] Since this voltage is considerably higher than the. with standvoltage in a normal MOS process, a high withstand voltage process for anLDD (lightly doped drain-source) structure or the like is applied to aliquid crystal driving transistor formed in each pixel on the silicondriving circuit substrate. Considering the production cost, powerconsumption and so forth, the withstand voltage is generally in a rangeof 8 to 12V. This is the reason that the known device is so designed asto have a V-T curve of ±4 to 6V at the maximum.

[0008] In the vertically-aligned liquid crystal material used in theknown devices, the refractive index anisotropy Δn (=n(∥)−n(⊥), which isthe difference between the refractive index n(∥) along the major axis ofthe liquid crystal molecule and the refractive index n(⊥) verticalthereto), has a value less than 0.1 (typically 0.08 or so), and thetypical pixel pitch is 13.5 μm (pixel size 13 μm).

[0009] Recently, one defect of the liquid crystal display deviceconcerning a low response speed thereof is attracting attention as aproblem, and it is well known that raising the response speed is animportant requisite. In general, the response speed (rise time and falltime) of the liquid crystal is proportional to the square of thethickness d of the liquid crystal layer, as expressed by Eq. (1) and Eq.(2) below. Therefore, reducing the thickness of the liquid crystal layeris effective to attain a higher response speed. $\begin{matrix}{{{rise}\quad {{time}:{\tau \quad {on}}}} = \frac{\gamma \cdot d^{2}}{{ɛ(0)}\Delta \quad \left( {V^{2} - {Vc}^{2}} \right)}} & (1) \\{{{fall}\quad {{time}:{\tau \quad {off}}}} = \frac{\gamma \cdot d^{2}}{K \cdot \pi^{2}}} & (2)\end{matrix}$

[0010] (where γ: viscosity of liquid crystal, d: thickness of liquidcrystal layer, Δε: permittivity anisotropy of liquid crystal, ε(0):space permittivity, K: elastic constant of liquid crystal, V: voltageapplied to liquid crystal (liquid crystal driving voltage), Vc:threshold voltage).

[0011] However, in the vertically-aligned liquid crystal display deviceknown heretofore, although the response speed thereof is rendered higheraccording to Eqs. (1) and (2) with reduction of the thickness of theliquid crystal layer, there arises another problem that the drivingvoltage required for saturating the transmissivity becomes higher. FIG.15 graphically shows V-T curves obtained by reducing the thickness ofthe liquid crystal layer in a system using a liquid crystal material(where Δn=0.082) employed in a conventional device, and FIG. 16graphically shows changes caused in the saturation voltage with thethickness d of the liquid crystal layer.

[0012] As shown in FIGS. 15 and 16, the saturation voltage of the devicebecomes sharply higher over 6V after the thickness d of the liquidcrystal layer is reduced to less than 2.5 μm, and the saturation voltagereaches high as 10V or so when the thickness d is less than 2 μm. Thatis, the withstand voltage required for the driving transistor needs tobe higher than 20V. In addition, when the thickness d is less than 1.5μm, the absolute value of the transmissivity fails to reach 100%. Incase the thickness d is 1 μm, the transmissivity attainable is merely30% or so, while the threshold voltage is raised to be higher.

[0013] Such a phenomenon is considered to result from that, with areduction of the thickness d (cell gap) in the vertically-aligned liquidcrystal, the interaction exerted on the interface between the liquidcrystal molecules and the orientation film becomes relatively greater tothe directional change caused in the director of the liquid crystalmolecules by the applied voltage. To the contrary, when the liquidcrystal layer has a sufficient thickness, the director is rendered moremobile due to the property as a bulk, whereby the interaction on theinterface is decreased in effect.

[0014] As described above, if the driving voltage becomes higher in theliquid crystal display device, proper driving fails to be performed inan ordinary driving device substrate of silicon. It is a matter ofcourse that this problem can be solved by raising the withstand voltageof the pixel driving transistor, but generally the process iscomplicated with further disadvantages of increasing both the productioncost and the power consumption. Further due to such a rise of thewithstand voltage, it is unavoidable that the transistor size isenlarged. For this reason, it becomes extremely difficult to manufacturehigh withstand-voltage transistors in a small pixel size (or pitch) lessthan 10 μm or so in particular.

[0015] For the reason mentioned above, it is practically difficult, inany known reflex display device using the conventionalvertically-aligned liquid crystal, to reduce the thickness of the liquidcrystal layer to less than 2.5 μm.

[0016] Reducing the thickness of the liquid crystal layer as describedslows down the rise (response speed) to the applied voltage and lowersthe yield in manufacture of the device.

[0017] Further, in any projection optical system equipped with suchknown display device, the F number of the optical unit needs to be equalto or greater than 3.5 for maintaining a high contrast as will beexplained below, hence bringing another problem that a high luminance isnot attained.

[0018] In any projection system equipped with reflex liquid crystaldisplay devices, as shown in. FIG. 17, there is required an optical unitwherein luminous flux emitted from a lamp light source 1 is irradiatedto reflex liquid crystal display devices 3R, 3G, 3B, each usingvertically-aligned liquid crystal, via polarized beam splitters 2R, 2G,2B which serve as polarized light separating devices for red (R), green(G) and blue (B) respectively, and the reflected light beams modulatedby such devices are collected by a prism (X-cube prism) 4 whichsynthesizes the light beams of the individual colors, and then thecomposite light beam is projected as projection light 10(p) to anunshown screen via a projection lens 5.

[0019] Here, in an illumination optical unit for illuminating the reflexliquid crystal devices 3R, 3G, 3B, the white light (10(p,s) composed ofp-polarized component and s-polarized component) from the white lamplight source 1 is processed to be s-polarized light 10(s) via a fly-eyelens 6, a polarizer/converter 7, a condenser lens 8 and so forth.Subsequently the s-polarized light 10(s) is introduced to a dichroiccolor separation filter 9, and the light separated therethrough is sentto total reflection mirrors 11, 12 and a dichroic mirror 13 toconsequently become light 10R(s), 10G(s) and 10B(s) of individualcolors. Thereafter the light is incident upon the reflex liquid crystaldisplay devices 3R, 3G, 3B respectively via the polarized beam splitters2R, 2G, 2B, and the reflected light is polarized and modulated inaccordance with the voltage applied to the reflex liquid crystal displaydevices 3R, 3G, 3B. After incidence upon the polarized beam splitters2R, 2G, 2B again, only the p-polarized components 10R(p), 10G(p), 10B(p)of the light are transmitted and then are synthesized by the prism 4.Consequently, when the applied voltage is zero in the reflex liquidcrystal display device, the incident light is reflected directly ass-polarized light without passing through the polarized beam splitter,and thus the system is placed in a normally black mode where the lightis polarized and modulated with a rise of the applied voltage, so thatthe p-polarized reflected light is increased to eventually raise thetransmissivity (refer to FIG. 14).

[0020] In the optical unit employed for the known vertically-alignedliquid crystal display device reported in Papers (1) and (2), the Fnumber is equal to or greater than 3.5 (e.g., 3.8 to 4.8 in Paper (1),or 3.5 in Paper (2)). The F number of the optical unit is a function ofthe incidence angle (outgoing angle of reflected light) θ of the lightincident upon the device, and it is expressed as follows.

F=1/(2×sin θ)   (3)

[0021] An expression of F=3.5 signifies that the device face isilluminated by the light within an angle of θ=±8.2° centering around aline perpendicular to the device face, and the reflected light isobtained therefrom.

[0022] As obvious from Eq. (3), the smaller the F number, the lightincidence and outgoing angle θ become greater to consequently increasethe total luminous flux, hence raising the luminance. However, in thereflex liquid crystal device, generally the black level value(transmissivity in a black state) becomes higher with an increase of theincidence angle, and the polarized-light separation characteristic ofthe polarized beam splitter is dependent on the angle θ, whereby it isunavoidable that the characteristic is deteriorated with an increase ofthe angle θ, and the degree of separation into the p-polarized lightcomponent and the s-polarized light component is rendered lower when theangular component is great. For the reasons mentioned, there occurs aphenomenon that the black level rises while the contrast is considerablylowered.

[0023] Thus, in practical use, there exists a problem of trade-off(difficulty for compatibility) between the luminance and the contrast.Because of this problem, in any conventional projection system equippedwith such a known device, there is employed an optical unit where the Fnumber is greater than 3.5 (more specifically, the F number of theprojection lens 5 or that of the illumination optical unit). That is, inany projection optical system equipped with the known device, the Fnumber is not settable to less than 3.5 due to a demand for practicallyrealizing a high contrast to a certain degree, hence causing a failurein raising the luminance.

[0024] It is therefore a first object of the present invention toprovide improvements in a vertically-aligned liquid crystal displaydevice which is represented by a reflex liquid crystal display device ofthe invention having a high response speed, wherein the liquid crystaltransmissivity reaches saturation at a low voltage despite a smallthickness of the liquid crystal layer, and the device can be driven withfacility on a driving circuit substrate manufacturable by an ordinarywithstand voltage process even in a small pixel size. The aboveimprovements also connote a display apparatus, a projection opticalsystem and a projection display system using such a reflex liquidcrystal display device of the invention.

[0025] A second object of the present invention resides in providing aprojection optical system and a projection display system where asufficiently low black level can be maintained in addition to the aboveaccomplishment even in a high-luminance optical unit having a small Fnumber, hence achieving a practically high contrast (i.e., meeting therequirements for both a higher luminance and a higher contrast incomparison with those of any conventional system).

DISCLOSURE OF INVENTION

[0026] More specifically, the reflex liquid crystal display device ofthe present invention is such that a first substrate having a lighttransmissive electrode and a second substrate having a light reflectiveelectrode are positioned opposite to each other in a state where thelight transmissive electrode and the light reflective electrode aremutually opposed while a vertically-aligned liquid crystal layer isinterposed therebetween. In this display device, the vertically-alignedliquid crystal layer has a thickness of less than 2 μm, and thevertically-aligned liquid crystal material has a refractive indexanisotropy Δn of more than 0.1. Here, the definition of “lightreflective electrode” signifies an electrode being reflective itself tolight, an electrode having a light reflective layer thereon, and also anelectrode which may be transmissive itself to light but has an undercoatfilm on condition that light reflectivity is effected in the interfacebetween the electrode and the undercoat film.

[0027] The present invention relates also to a display apparatusequipped with the reflex liquid crystal display device of the invention,and further to a projection optical system where the reflex liquidcrystal display device is disposed in its optical path, and a projectiondisplay system using such an optical system.

[0028] According to the present invention, although thevertically-aligned liquid crystal layer is less than 2 μm in thickness,the value Δn of the vertically-aligned liquid crystal material isadjusted to be more than 0.1 differently from the conventionalrecognition, so that the transmissivity of the liquid crystal reachesits saturation with facility at a voltage lower than 5-6V, henceenabling satisfactory driving at a practically low voltage and muchenhancing the transmissivity itself. Consequently, it becomes possibleto achieve improvements in the reflex vertically-aligned liquid crystaldisplay device having a sufficient transmissivity and superior drivingcharacteristic with low-voltage driving (low required withstand voltage)while holding a high response speed, and also in a display apparatus, aprojection optical system and a projection display system using suchimproved display device.

[0029] The remarkable advantageous functions and effects mentioned aboveare obtainable due particularly to the selective use of avertically-aligned liquid crystal material having a value Δn of morethan 0.1. In case the liquid crystal layer is reduced in thickness toless than 2 μm for attaining a high response speed, if the directionalchange of the director is to be affected by the interaction between theorientation film and the liquid crystal molecules, the incident light isprone to be polarized and modulated, since Δn is greater than 0.1, inthe liquid crystal in compliance with the applied voltage to eventuallycause ready separation of the polarized light, whereby the desiredtransmissivity can be obtained even at a low voltage.

[0030] The present invention also provides a projection optical systemwhere the reflex liquid crystal display device of the invention and anoptical unit having an F number of less than 3 are disposed in itsoptical path, and further provides a projection display system usingsuch an optical system.

[0031] According to the above systems, a black level supposed to beproportional to the square of the thickness of the liquid crystal layercan be kept low as the thickness of the vertically-aligned liquidcrystal layer is set to less than 2 μm, and therefore a high contrastcan be realized even if the F number of the optical unit is less than 3,and yet a high luminance is also attainable with such a small F number.Thus, the projection optical and display systems, each of which isequipped with the reflex liquid crystal device of the invention and anoptical unit having an F number under 3, satisfy the requirements for ahigher contrast and a higher luminance in comparison with those of anyconventional system using the known device and optical unit. The Fnumber of the optical unit is controllable by the focal distance and soforth of a lens used therein.

BRIEF DESCRIPTION OF DRAWINGS

[0032]FIG. 1 graphically shows V-T curves obtained by changing therefractive index anisotropy Δn of a vertically-aligned liquid crystalmaterial in a reflex liquid crystal display device (where the thicknessd of a liquid crystal layer is 2 μm);

[0033]FIG. 2 graphically shows V-T curves obtained by changing therefractive index anisotropy Δn of a vertically-aligned liquid crystalmaterial in a reflex liquid crystal display device (where the thicknessd of a liquid crystal layer is 1.5 μm);

[0034]FIG. 3 graphically shows V-T curves obtained by changing therefractive index anisotropy Δn of a vertically-aligned liquid crystalmaterial in a reflex liquid crystal display device (where the thicknessd of a liquid crystal layer is 1 μm);

[0035]FIG. 4 graphically shows the response speeds of a reflexvertically-aligned liquid crystal display device (where samples being 3μm and 3.5 μm thick indicate values of known devices);

[0036]FIG. 5 is a table of data representing the saturation voltage,transmissivity and response speed of each sample obtained in relation tothe thickness d, refractive index anisotropy Δn and permittivityanisotropy Δε of a vertically-aligned liquid crystal material in areflex liquid crystal display device;

[0037]FIG. 6 graphically shows comparative changes of the saturationvoltage with the refractive index anisotropy Δn of the same liquidcrystal in relation to the thickness d of the liquid crystal layer;

[0038]FIG. 7 graphically shows V-T curves obtained when the thickness ofthe same liquid crystal layer is 3.5 μm and the refractive indexanisotropy Δn of the liquid crystal is 0.13;

[0039]FIG. 8 graphically shows the dependency of the black-statetransmissivity on the thickness of the same liquid crystal layer (incomparison with the black-state value as 100% of a liquid crystal layerbeing 3.5 μm thick in a known device);

[0040]FIG. 9 graphically shows the black level changes caused in thereflex vertically-aligned liquid crystal device of the present inventionin comparison with the black level changes relative to the F number of ameasuring optical unit in the known device;

[0041]FIG. 10 graphically shows the luminance changes caused in the sameliquid crystal device relative to the F number;

[0042]FIG. 11 is a schematic sectional view of the reflexvertically-aligned liquid crystal display device of the presentinvention;

[0043]FIG. 12 is a sectional view of principal portions on a drivingcircuit substrate of silicon in the display device of the invention;

[0044]FIG. 13 is an equivalent circuit diagram with the layout of thedisplay device of the invention;

[0045]FIG. 14 graphically shows a V-T curve of the known device (wherethe thickness of its liquid crystal layer is approximately 3 μm);

[0046]FIG. 15 graphically shows V-T curves obtained while reducing thethickness of the liquid crystal layer in the known device (whereΔn=0.082);

[0047]FIG. 16 graphically shows the changes caused in the saturationvoltage in accordance with the thickness of the same liquid crystallayer; and

[0048]FIG. 17 is a schematic diagram of a projection optical systemusing the known reflex liquid crystal display device.

BEST MODE FOR CARRYING OUT THE INVENTION

[0049] In the reflex liquid crystal display device of the presentinvention, the thickness of the vertically-aligned liquid crystal layerneeds to be equal to or less than 2 μm for achieving the functionaleffects mentioned above. It is more preferred that the thickness be in arange of 0.8 to 2 μm, and further in a range of 1 to 2 μm. Although theresponse speed is raised with a reduction of the layer thickness, thelower limit of the thickness is preferably 0.8 μm, and more preferably 1μm in regard to suppression of the interaction to the orientation filmand also in regard to controllability of the layer thickness. While thethickness of the liquid crystal layer may be small, Δn needs to begreater than 0.1 in order to enhance the polarized light separation, butan excessive increase of Δn is not exactly efficient for enhancing theeffect or is not practical either. Therefore, Δn may preferably be lessthan 0.25.

[0050] In a preferred structure, a liquid crystal orientation film isformed on the opposed face of a transparent electrode of ITO (indium tinoxide) or the like as the aforementioned light transmissive electrodeand also on the opposed face of the light reflective electrode ofaluminum or the like, and the light reflective electrode is connected toa single crystal semiconductor driving circuit of silicon or the likeprovided on the aforementioned second substrate, thereby constituting anactive driving type. If a driving circuit substrate of silicon isemployed as the second substrate, the substrate itself is opaque andadapted for reflex type. Moreover, a MOS (metal oxide semiconductor)transistor as a driving element and an auxiliary capacity for voltagesupply are suited for high-density integration attained with a minutepattern by the semiconductor processing technology, so that it becomespossible to realize a high aperture rate, a high resolution due toenhancement of a pixel density, reduction of a cell size, andenhancement of a carrier transfer rate.

[0051] Actually, the driving circuit comprises a driving transistor suchas MOSFET (metal oxide semiconductor field effect transistor) providedfor each pixel on the silicon substrate, and the light reflectiveelectrode is connected to the output side of the driving transistor. Thepixel size can be reduced to equal to or less than 10 μm due to the useof a low withstand voltage transistor which is drivable at a lowvoltage. And the liquid crystal display device is also reducible in sizeto equal to or less than 2 inches diagonally.

[0052] Orientation control of the vertically orientated liquid crystalmaterial may preferably be performed by means of a liquid crystalorientation film composed of a silicon oxide film. Such an orientationfilm can be formed by vacuum evaporation or the like with directivity(i.e., capable of easily controlling the pretilt angle of liquid crystalmolecules).

[0053] In a display apparatus equipped with the reflex liquid crystaldisplay device of the present invention and also in projection opticaland display systems where such liquid crystal display device is disposedin the optical path thereof (further with an optical unit having an Fnumber under 3), a light source and an optical unit for enablingincidence of the light from the light source onto the reflex liquidcrystal display device may preferably be disposed in the optical pathtogether with the reflex liquid crystal display device and anotheroptical unit for introducing the reflected light from the reflex liquidcrystal display device.

[0054] In this case, it is preferred that the light emitted from thelight source is incident upon the reflex liquid crystal display devicevia a polarizer/converter and a polarized beam splitter, and thereflected light from the reflex liquid crystal display device isintroduced via the polarized beam splitter again or is introducedfurther via a projection lens to a screen.

[0055] It is also preferred that the reflex liquid crystal displaydevice and the polarized beam splitter are disposed for each of colors,and the reflected light components from the individual reflex liquidcrystal display devices are synthesized or are introduced further to theprojection lens. More concretely, white light emitted from a white lightsource is introduced via the polarizer/converter to a dichroic colorseparating filter, which then separates the light into respective lightcomponents of the individual colors. Subsequently, the light componentsare incident upon the reflex liquid crystal display devices respectivelyvia the polarized beam splitter, and the reflected light componentstherefrom are synthesized by means of a prism.

[0056] Here, the F number of the optical unit used in combination withthe reflex liquid crystal display device of the invention needs to be asmall value of less than 3 for attaining compatibility of a highcontrast and a high luminance. Preferably, however, the F number isdesired to be not more than 3.0 and not less than 1.5 (further not lessthan 2.0) in order to enhance the effect.

[0057] Now a preferred embodiment of the present invention will bedescribed below in detail with reference to the accompanying drawings.

[0058] First, FIG. 11 shows the fundamental configuration of a liquidcrystal electro-optical device constituting a display apparatus which isrepresented by the preferred embodiment.

[0059] This device serving as a reflex liquid crystal display device 23comprises a silicon driving circuit substrate 31 composed of singlecrystal of silicon or the like and having a light reflective electrode30 of a pixel structure, and a transparent substrate 33 of glass or thelike having a transparent electrode 32 and positioned opposite to thesubstrate 31, wherein a vertically-aligned liquid crystal 36 is sealedbetween the two substrates (actually between liquid crystal orientationfilms 34 and 35). As shown in FIG. 12, a reflective electrode substrateserving as the driving circuit substrate is such that a driving circuitcomprising CMOS and n-channel MOS transistors Tr and capacitors C isformed on a single crystal silicon substrate 37, and a light reflectiveelectrode 30 of a pixel structure is formed thereon with a metal film ofaluminum, silver or the like. In case the light reflective electrode iscomposed of metal such as aluminum, it functions as both a lightreflecting film and an electrode to apply a voltage to the liquidcrystal. For the purpose of further raising the light reflectivity, alight reflective layer with a multi-layer film such as a dielectricmirror may also be formed on the aluminum electrode.

[0060] In FIG. 12, the transistor Tr comprises, for example, an n-typesource region 38, a drain region 39, a gate insulating film 40 and agate electrode 41, wherein electrodes 42 and 43 are led out from theactive regions respectively. In this structure, the electrode 43 isconnected via an inter-layer insulating film 47 to a capacitor electrode46 which is in contact with an insulating film (dielectric film) 45 onan n-type region 44 constituting a capacitor C. The electrode 43 isconnected also to a wire 50 via inter-layer insulating films 48, 49 andfurther to the light reflective electrode 30. In this device, thes-polarized incident light 10(s) shown in FIG. 17 is converted inaccordance with the applied voltage in the layer of thevertically-aligned liquid crystal 36, whereby reflected light 10(p)including p-polarized light is obtained, and then the light 10(p) isintroduced to the aforementioned polarized beam splitter 2.

[0061] In the reflex liquid crystal display device of the presentinvention, the layer thickness d (cell gap) of the vertically-alignedliquid crystal 36 is set to be equal to or less than 2 μm, and therefractive index anisotropy Δn of the vertically-aligned liquid crystal36 employed here is more than 0.1.

[0062]FIG. 13 shows a fundamental layout of the display device and anequivalent circuit of its pixel portion. The silicon driving circuitsubstrate 31 comprises a pixel driving circuit formed in each pixel, anda logic driver circuit (data driver, scanning driver and so forth)incorporated in the periphery of a display area. The pixel drivingcircuit formed under each light reflective (pixel) electrode 30 consistsof a switching transistor Tr and an auxiliary capacitance C forsupplying a voltage to the vertically-aligned liquid crystal 36. Thetransistor Tr is required to withstand a predetermined voltagecorresponding to the driving voltage for the vertically-aligned liquidcrystal, and it is produced normally by a higher withstand voltageprocess as compared with the logic. Since the transistor size becomesgreater with a rise of the withstand voltage, usually a transistorhaving a withstand voltage of 8 to 12V or so is used in view of theproduction cost and the power consumption. Therefore, it is desired todesign that the liquid crystal driving voltage is set within ±6V. Thisrequirement can be met according to the present invention.

[0063] In the vertically-aligned liquid crystal 36 used in this displaydevice, each molecule is so oriented that the major axis thereof isrendered substantially vertical to the substrate when no voltage isapplied, and upon application of a voltage, the major axis is inclinedto the in-plane direction to thereby change the transmissivity. If theinclinations of the liquid crystal molecules are not the samedirectionally when the liquid crystal is driven, there occurs somenon-uniformity in brightness and darkness. In order to avoid such adisadvantage, it is necessary to vertically orient the liquid crystal bypreviously giving a slight pretilt angle in a fixed direction (generallyin the diagonal direction of the device) as shown in FIG. 11.

[0064] If the pretilt angle is excessively large, the verticalorientation characteristic is deteriorated with a rise of the blacklevel to eventually lower the contrast while affecting the V-T curve.Therefore, the pretilt angle is controlled generally within a range of1° to 7°. Each of the liquid crystal orientation films 34 and 35 to begiven such a pretilt angle is composed of a silicon oxide filmrepresented by SiO₂, such as an oblique evaporated film, or a polyimidefilm. In the former, the evaporation angle given at the time of obliqueevaporation is in a range of 45° to 55°; meanwhile in the latter, thepretilt angle is controlled within a range of 1° to 7° by changing therubbing condition.

[0065] In the known device, the thickness d of the vertically-alignedliquid crystal layer in the device structure of FIG. 11 is approximately3 to 4 μm, and there is used a selected liquid crystal material wherethe refractive index anisotropy Δn is less than 0.1 (typically 0.08 orso). However, if the thickness d of the liquid crystal layer in theknown device is reduced to less than 2.5 μm, the response speed isrendered higher but the driving voltage is raised as described above, sothat the requirements for practical use fail to be satisfied. Themechanism of this phenomenon that the driving voltage is raised withreduction of the thickness of the liquid crystal layer is not exactlydefinite, but it is considered to be derived from that, while the bulkproperty of the liquid crystal appears principally with an increase ofthe layer thickness, the influence of the interaction on the interfacebetween the orientation film and the liquid crystal is not negligible(i.e., the interaction is supposedly so exerted as not to incline theliquid crystal molecules).

[0066] As the result of repeating many experiments in order to overcomethe problems mentioned above, the inventor has found that the problemscan be solved by selectively controlling the refractive index anisotropyΔn of the vertically-aligned liquid crystal material to more than 0.1.FIGS. 1 and 2 graphically show V-T curves obtained by changing theanisotropy Δn of the liquid crystal under conditions that the thicknessd of the liquid crystal layer is 2 μm and 1.5 μm, respectively. It isseen from these diagrams that, despite reduction of the thickness d ofthe liquid crystal layer to less than 2 μm in particular, thetransmissivity is easily saturated at a low voltage of 4 to 6V or lessif the anisotropy Δn is held over 0.1, whereby practical driving isachievable.

[0067] According to the present invention, even in a display devicewhere the thickness d of its liquid crystal layer is extremely small as1 μm, the transmissivity is saturated at a low driving voltage of 6V orso if the anisotropy Δn is held over 0.1, as shown in FIG. 3. It is alsoseen that remarkable improvements can be attained in comparison with anyconventional device where the transmissivity obtained by using the knownmaterial composition is merely 30% or so. Particularly due to the use ofa selected liquid crystal material having a high value of Δn=0.13, it ispossible to realize, even with a thickness of 1 μm, an excellent reflexdisplay device which uses vertically-aligned liquid crystal of siliconand indicates a sufficient transmissivity with superior drivingcharacteristic.

[0068]FIG. 4 graphically shows the response speed (rise time+fall time)of the reflex liquid crystal display device according to the presentinvention. As plotted, the response is much faster in comparison withthat in any conventional device, such as 7 to 9 msec with d=2 μm, orunder several msec with d=1.5 μm or less. (However, with d=2.5 μm, theresponse speed is lowered to 13-14 msec.) In the device with d=1.5 μm orless, the fast response is kept under 8 msec even in a half tone. Thisdevice is capable of realizing a satisfactory image quality even inmotion pictures of movies or television pictures where half-tone displayis frequently employed with many moving images.

[0069]FIG. 5 is a table showing the characteristics of the displaydevice (samples Nos. 7-15) of the present invention and those ofcomparative examples (samples Nos. 1-6, 16-19). FIG. 6 graphically showschanges of a saturation voltage with Δn in relation to the thickness dof a liquid crystal layer. In view of the driving characteristic, thetransmissivity and the response speed, suitable values adapted forpractical use are as follows. The thickness d of the liquid crystallayer is preferably less than 2 μm, and particularly 1 to 2 μm; Δn ofthe liquid crystal with d =2 μm is preferably Δn≧0.1 (more preferablyΔn≧0.103, further preferably Δn≧0.114); with d=1.5 μm, Δn≧0.106 (morepreferably Δn≧0.11, further preferably Δn≧0.114); and with d=1 μm,Δn≧0.104 (more preferably Δn≧0.114, further preferably Δn≧0.12).

[0070]FIG. 7 graphically shows V-T curves obtained when the thickness ofthe liquid crystal layer in the known device is 3.5 μm by the use of avertically-aligned liquid crystal material having a high refractiveindex anisotropy Δn of more than 0.1, i.e., in the case of Δn=0.13 forexample. As seen from this graph, the threshold voltage is considerablylowered, and saturation is attained at a driving voltage ofapproximately 2V. However, as obvious from the aforementioned Eq. (1),the response speed is in inverse proportion to the square of the drivingvoltage while being changed in conformity with the thickness d of theliquid crystal layer, so that such a low driving voltage extremelydeteriorates the response speed. According to the results of actualmeasurements, the black-and-white response speed of this device is 46msec (approx. 50 msec), and in a half tone, the response speed islowered to 100 msec or so due to a further drop of the driving voltage,hence causing manifest difficulty for practical use. Thus, in the knowndevice, it is necessary to reduce the value of Δn under 0.1 in view ofthe response speed.

[0071] As described above, the present invention has been accomplishedby newly finding the requisite value of Δn of the liquid crystalmaterial so as to realize an improved reflex vertically-aligned liquidcrystal device where the thickness d of its liquid crystal layer is lessthan 2 μm. Therefore, even if the thickness d of the liquid crystallayer is less than 2 μm, the saturation voltage can be lowered byselectively adjusting the refractive index anisotropy as Δn≧0.1, henceenhancing the response speed as well.

[0072] The table shown below gives the values of Δn (also those of Δε)of vertically-aligned liquid crystal materials (made by Merck Ltd.,).Vertically-aligned liquid crystal material Sample A Sample B Sample CSample D Δn +0.082 +0.103 +0.114 +0.13 n (∥) 1.557 1.584 1.598 1.62 n(⊥) 1.475 1.481 1.484 1.49 Δ ε −4.1 −0.5 −5.3 −4.3 ε (∥) 3.5 4.0 3.9 3.8ε (⊥) 7.6 9.0 9.2 8.1

[0073] Next, a description will be given on the advantage that thevertically-aligned liquid crystal display device of the invention ismore effective for an optical unit of a smaller F number as comparedwith any known device.

[0074] First, it has been found that the black level in the device ofthe invention having a thinner liquid crystal layer can be lowered underthe black level obtained in the known device where the liquid crystallayer has a thickness of 3 to 4 μm. In FIG. 8, each black level value(black-state transmissivity at zero voltage) in the vertically-alignedliquid crystal display device of the invention is graphically shown as afunction of the thickness of the liquid crystal layer. In the respectivematerials, the numerical values obtained with a layer thickness of 3.5μm are expressed as 100% (where the abscissa represents the thickness ofthe liquid crystal layer).

[0075] When the applied voltage is zero, the liquid crystal moleculesare oriented to be substantially vertical to the substrate plane, sothat in principle the incident light is reflected without any change ofthe polarized state and then is returned to the incidence side by meansof a polarized beam splitter. However, in the actual device, the liquidcrystal molecules are inclined at a pretilt angle and are thereforerendered slightly elliptical, and moreover the light separationcharacteristic of the polarized beam splitter is dependent on theincidence angle as mentioned, whereby the black-state transmissivity israised to consequently deteriorate the contrast.

[0076] Meanwhile in the display device of the present invention, it hasbeen found that the black-state transmissivity is lowered with areduction of the thickness of the liquid crystal layer and, as shown inFIG. 8, the black level value obtained with a layer thickness of 2 μmbecomes 20-30% as compared with the value in the known device, or 10-20%with a layer thickness of 1.5 μm, or 5-15% with a layer thickness of 1.0μm. (But when the layer thickness is 2.5 μm, the black level valuebecomes high as 40-50%). Regarding the contrast which is expressed bythe ratio of white and black levels, since the white level is keptsubstantially unchanged, the result shown in FIG. 8 indicates that thecontrast attained in the device of the present invention becomes higherthan five to ten times or more with a layer thickness of 1.5 μm forexample.

[0077] Such fall of the black level value with a reduction of thethickness of the liquid crystal layer is considered to be basedprincipally on the following reasons. The transmissivity T of the liquidcrystal in the device of the present invention is expressed by Eq. (4).

T∝ sin²(2d·Δn(eff)·π/λ)   (4)

[0078] In the above, λ denotes the wavelength of the light, and Δn(eff)denotes the effective refractive index anisotropy corresponding to theinclination angle θ from the perpendicular direction of liquid crystalmolecules. This anisotropy is expressed by Eq. (5). $\begin{matrix}{{\Delta \quad {n({eff})}} = {\frac{{n\left( {\quad } \right)}{n(\bot)}}{\sqrt{\left\lbrack {{{n\left( {\quad } \right)}^{2} \cdot {\cos^{2}(\theta)}} + {{n(\bot)}^{2} \cdot {\sin^{2}(\theta)}}} \right\rbrack}} - {n(\bot)}}} & (5)\end{matrix}$

[0079] The inclination angle θ of the liquid crystal molecules iswidened with a rise of the liquid crystal driving voltage, and Δn(eff)is increased correspondingly thereto to raise the transmissivityconsequently. It is seen that, when θ=90° in principle, Δn(eff) becomesequal to the value of Δn of the liquid crystal material. According toEq. (4), the transmissivity T becomes 100% when the condition of2d·Δn(eff)·π/λ=π/2 is satisfied.

[0080] The black level value, i.e., the transmissivity in a black state,becomes zero if the liquid crystal molecules are oriented completelyvertically as (θ=0), so that Δn(eff)=0. Actually, however, the liquidcrystal molecules are oriented with a pretilt angle of 1 to 7° asmentioned, whereby the value of Δn(eff) is rendered finite toconsequently give the black-state transmissivity. As the black-statetransmissivity is raised with an increase of the pretilt angle, it ispreferred that the pretilt angle be controlled to less than 5°. Since2d·Δn(eff)·π/λ has a small value at the black level, Eq. (4) may berewritten approximately as

T∝ sin²(2d·Δn(eff)·π/λ)≈(2d·Δn(eff)·π/λ)².

[0081] Therefore, T is theoretically considered to be proportional tothe square of the thickness d of the liquid crystal layer. The data ofFIG. 8 obtained from the actual measurement can be explainedsubstantially in accordance with this relation.

[0082] Thus, the thickness d of the liquid crystal layer in this deviceis so designed as to be less than 2 μm, and therefore the black levelcan be suppressed low essentially in comparison the known device wherethe layer thickness is 3 to 4 μm, hence realizing a high contrast.

[0083] If the F number of the optical unit is decreased in the knowndevice, the black level is raised to eventually fail in ensuring adesired contrast, and therefore it is unavoidable to set the F numberforcedly to more than 3.5, as already described. However, in the deviceof the present invention, the black level in the device itself is heldextremely low as explained, so that a sufficiently high contrast can beensured even in the optical unit having a small F number.

[0084]FIG. 9 graphically shows changes caused in the black-statetransmissivity by changing the F number of the projection lens 5 in FIG.17 and that of the measuring optical unit corresponding to theillumination optical unit. The black level rises with a decrease of theF number, but in the device of the present invention, the black level iskept lower than in the known device at any F number, whereby asufficiently high contrast can be realized even in the optical unithaving a smaller F number under 3. Moreover, a satisfactory highluminance is still attained with an F number of less than 3, as shown inFIG. 10. (However, the luminance is saturated when the F number is under2). And the luminance is considerably lowered if the F number exceeds 3.

[0085] Regarding the luminance, it has been found experimentally that,in a practical projection system with an optical unit using a 120 W lampin a diagonally 0.7-inch device for example, the luminance is enhancedapproximately 60% when the F number is changed from 3.85 to 2.

[0086] As mentioned above, a superior projection system, which iscapable of meeting the requirements for both a higher contrast and ahigher luminance in comparison with any known system using theconventional device and optical unit, can be provided due to the displaydevice of the present invention and also to a projection optical systemand a projection display system each employing an optical unit of an Fnumber under 3.

[0087] Hereinafter the preferred embodiment of the present inventionwill be described more specifically with some comparative examples.

COMPARATIVE EXAMPLE 1

[0088] Each conventional known device was produced as follows. First, aglass substrate with a transparent electrode and a driving circuitsubstrate of silicon with an aluminum electrode were washed and thenwere introduced into an evaporator, where a liquid crystal orientationfilm of SiO₂ was formed by oblique evaporation in an angular range of 45to 55°. The thickness of the liquid crystal orientation film was set to50 nm, and the pretilt angle of the liquid crystal was so controlled asto be approximately 2.5°.

[0089] Thereafter an adequate number of glass beads having a diameter of1 to 3.5 μm were sprinkled between the two substrates where the liquidcrystal orientation film was formed, and the two substrates were joinedtogether. Subsequently, a vertically-aligned liquid crystal material(made by Merck Ltd.,) having a negative permittivity anisotropy Δε and arefractive index anisotropy Δn of 0.082 was injected between thesubstrates to thereby produce six kinds of reflex liquid crystal displaydevices (samples Nos. 1-6 in FIG. 5) where the liquid crystal layerthickness (cell gap) was 3.5 μm, 2.9 μm, 2.5 μm, 2 μm, 1.5 μm and 1 μmrespectively.

[0090] In each of the devices thus produced, a voltage was appliedbetween the transparent electrode and the aluminum electrode, and thechanges caused in the transmissivity of the liquid crystal by changingthe applied voltage were measured. (Since the devices are of reflextype, actually the reflectivity thereof is measured. However, measuringthe reflectivity is equivalent to measuring the transmissivity of theliquid crystal, and therefore it will be so described below.) Themeasurement was performed at room temperature.

[0091]FIG. 15 graphically shows the liquid crystal drivingcharacteristics of such devices. As shown in FIGS. 15 and 16, thesaturation driving voltage rises sharply over 6V when the thickness ofthe liquid crystal layer is less than 2.5 μm.

EMBODIMENT 1

[0092] In the same method as adopted for Comparative example 1 mentionedabove, a liquid crystal orientation film of SiO₂ was formed on each of asubstrate with a transparent electrode and a driving circuit substrateof silicon with an aluminum electrode, and three kinds ofvertically-aligned liquid crystal materials (made by Merck Ltd.,) havinga negative permittivity anisotropy Δε and a refractive index anisotropyΔn of 0.103, 0.114 and 0.13 were injected between the two substrates tothereby produce nine kinds of reflex liquid crystal display devices(samples Nos. 7-15 in FIG. 5) where the liquid crystal layer thickness(cell gap) was 2 μm, 1.5 μm and 1 μm respectively. The pretilt angle ofthe liquid crystal was so controlled as to be approximately 2.5°.

[0093] The liquid crystal driving characteristics of the devices thusproduced were measured at room temperature similarly to Comparativeexample 1. FIGS. 1, 2 and 3 graphically show the driving characteristicsobtained in three cases where the thickness of the liquid crystal layeris 2 μm, 1.5 μm and 1 μm respectively. FIG. 5 is a table showing thedriving voltages of the individual devices at which the transmissivityis saturated substantially, and also the respective values of thetransmissivity.

[0094] It is seen from such results that, as Δn is controlled to be morethan 0.1, the transmissivity is saturated easily at a low voltage of 4to 6V despite reduction of the liquid crystal layer thickness d under 2μm, whereby practical driving can be performed. Furthermore, since thetransmissivity is much enhanced in comparison with any conventionaldevice, it becomes possible to realize an improved silicon reflex typevertically-aligned liquid crystal display device having a sufficienttransmissivity and superior driving characteristic.

[0095] Other devices were also produced by forming, as a liquid crystalorientation film, a polyimide film instead of a silicon dioxide film,and controlling the orientation by rubbing. The results were the same asthose mentioned above.

EMBODIMENT 2

[0096] The response speed relative to a rise time (from black to white)and a fall time (from white to black) was measured in each of the reflexliquid crystal display devices produced in Embodiment 1. The sum totalthereof is regarded as the response speed of each device, and the resultis shown in FIG. 5. The measurement was performed at room temperature.FIG. 4 graphically shows the thickness d of the liquid crystal layer asa function with regard to the device having Δn=0.13 as a representativeexample (samples Nos. 9, 12, 15 with d=2.5 μm in FIG. 5). Forcomparison, FIG. 4 also shows the response speeds of the known sampleNo. 1 and the sample produced with d=3 μm (Δn=0.082 in each sample).

[0097] As supposed from Eqs. (1) and (2), the response speed changessubstantially in proportion to the square of the thickness of the liquidcrystal layer. In the device of the present invention where the layerthickness d is less than 2 μm and Δn is more than 0.1, it was proved torealize a high-speed response faster than 9 msec.

COMPARATIVE EXAMPLE 2

[0098] In the same method as adopted for Embodiment 1, a reflex liquidcrystal device (sample No. 16) was produced by using a liquid crystalmaterial of Δn=0.13 with a layer thickness of 3.5 μm, and the liquidcrystal driving characteristic was measured.

[0099]FIG. 7 graphically shows the result in comparison with thecharacteristic of sample No. 1 obtained with Δn=0.082. As shown, thedriving voltage in the device (sample No. 16) was much lower. Theresponse speed measured at room temperature in the same manner as inEmbodiment 2 was 46 msec. Since the driving voltage in a half tone islow as 1V or so, the response speed was rendered lower, and in agray-scale gradation of 25%, the response speed was further lowered tothe vicinity of 100 msec.

EMBODIMENT 3

[0100] The transmissivity (black level) at a zero applied voltage (blackstate) was measured in the reflex liquid crystal display device producedin Embodiment 1. For systematically examining the black level changescaused in relation to the thickness of the liquid crystal layer, deviceshaving a layer thickness of 3.5 μm (samples Nos. 17-19) were producedwith the aforementioned samples of Δn, and also devices having a layerthickness of 2.5 μm were produced similarly, and the black-leveltransmissivity of each device was measured together with the samples(Nos. 7-15) of Embodiment 1. The respective black level values aregraphically shown in FIG. 8 where the numerical values obtained in thedevices with a layer thickness of 3.5 μm are indicated as 100% with theindividual samples of Δn.

[0101] As shown in FIG. 8, the black level is extremely lowered when theliquid crystal layer becomes thinner than 2 μm in any sample of Δn. Inthe device with a layer thickness of 1.5 μm for example, the indicatedblack level is lower by 10 to 20% than the value obtained in any devicewith a layer thickness of 3.5 μm. That is, the contrast of the devicebecomes so high as 5 to 10 times. In the measuring optical unit of FIG.7 having an F number of 3.85, this trend remained substantially the samedespite any change of the F number.

EMBODIMENT 4

[0102] The devices (samples Nos. 12, 9) of Embodiment 1 with Δn=0.13 anda liquid crystal layer thickness of 1.5 am and 2.0 μm were incorporatedin the measuring optical unit having an F number of 3.85, 3 and 2, andthe black level (black-state transmissivity) of each device was comparedwith that of the known device (sample No. 1).

[0103]FIG. 9 graphically shows the results of such comparison. The blacklevel rises with a decrease of the F number. However, in the device ofthe present invention, the black level is maintained lower than that inthe known device despite any change of the F number. The white leveltransmissivity in each device was kept substantially unchanged at 0.6 orso. Therefore, the black level ratio directly gives the contrast ratioof the device. According to the device of the invention, it is seen thatin any optical unit having a small F number under 3, an equal or highercontrast can be realized as compared with the known device. The lowerlimit of the F number may be set preferably to 1.5, further preferablyto 2.0.

[0104] In conformity with the specification described above, adiagonally 0.7-inch silicon reflex type vertically-aligned liquidcrystal display device was produced, and the luminance obtained by theuse of a 120 W lamp as a light source was compared in a practicalprojection optical unit having an F number of 3.85, 3.5, 3, 2.5 and 2.The results are graphically shown in FIG. 10 where, as compared with theluminance obtained in an optical unit of F number=3.85, the luminance isenhanced about 32% with F number=3, about 44% with F number=2.5, about60% with F number=2, and sharply enhanced with F number≦3. However, theluminance was enhanced merely 15% or so with F number=3.5, or notchanged substantially with F number=1.5 as compared with the valueobtained with F number=2. Regarding the contrast, even in an opticalunit with F number≦3, the contrast attained was higher than the value inthe known device, as mentioned. That is, a superior projection systemwas realized to meet the requirements for both a higher luminance and ahigher contrast in comparison with those in the known device.

[0105] It is to be understood that the embodiments and examples of thepresent invention described above may be modified variously on the basisof the technical concept of the invention.

[0106] For instance, the structure, material and so forth of thecomponent parts of the reflex liquid crystal display device or those ofan optical or projection system equipped with such display device arenot limited merely to the aforementioned ones alone, and may be alteredwith a variety of modifications.

[0107] Thus, according to the present invention where the Δn of thevertically-aligned liquid crystal material is controlled to be more than0.1, the transmissivity of the liquid crystal is saturated with facilityat a low voltage below 5 to 6V despite a reduction of the thickness ofthe vertically-aligned liquid crystal layer to less than 2 μm, henceachieving satisfactory driving at a practically low voltage whileattaining another advantage of remarkable improvement in thetransmissivity itself. Therefore, it becomes possible to realize asuperior reflex type vertically-aligned liquid crystal display devicewhich indicates a sufficient transmissivity, an excellent low-voltagedriving characteristic (low required withstand voltage) and fastresponse as well. Further improvements are realizable in a displayapparatus, a projection optical system and a projection display systemby the use of such a display device.

[0108] In these systems where the thickness of the vertically-alignedliquid crystal layer is reduced to less than 2 μm, the black level,which is considered to be proportional to the square of the thickness ofthe liquid crystal layer, can be held low to thereby achieve a highcontrast even when the F number of the optical unit is less than 3, anda high luminance is also achievable with a small F number. Consequently,it becomes possible to provide a superior system which is capable ofsatisfying the requirements for both a high contrast and a highluminance.

What is claimed is:
 1. A reflex liquid crystal display device comprisinga first substrate with a light transmissive electrode, a secondsubstrate with a light reflective electrode, and a layer ofvertically-aligned liquid crystal material interposed between said firstand second substrates positioned opposite to each other in a state wheresaid light transmissive electrode and said light reflective electrodeare opposed mutually, wherein the thickness of said vertically-alignedliquid crystal layer is less than 2 μm, and the refractive indexanisotropy Δn of said liquid crystal material is more than 0.1.
 2. Thereflex liquid crystal display device according to claim 1, wherein aliquid crystal orientation film is formed on each of the mutuallyopposed faces of said light transmissive electrode being transparent andsaid light reflective electrode, and said light reflective electrode isconnected to a single-crystal semiconductor driving circuit of siliconor the like formed on said second substrate, thereby constituting anactive driving type reflex liquid crystal display device.
 3. The reflexliquid crystal display device according to claim 2, wherein saidsingle-crystal semiconductor driving circuit comprises a drivingtransistor provided for each pixel on a silicon substrate serving assaid second substrate, and said light reflective electrode is connectedto the output side of said driving transistor.
 4. The reflex liquidcrystal display device according to claim 1, wherein the pixel size isless than 10 μm.
 5. The reflex liquid crystal display device accordingto claim 2, wherein a silicon oxide film is formed as said liquidcrystal orientation film.
 6. A display apparatus equipped with thereflex liquid crystal display device according to any of claims 1 to 5.7. The display apparatus according to claim 6, comprising a lightsource, an optical unit for enabling incidence of the emitted light fromthe light source onto the reflex liquid crystal display device, saidreflex liquid crystal display device, and an optical unit forintroducing the reflected light from said reflex liquid crystal displaydevice, wherein all of said components are disposed in an optical pathof said apparatus.
 8. The display apparatus according to claim 7,wherein the light emitted from said light source is incident upon saidreflex liquid crystal display device via a polarizer/converter and apolarized beam splitter, and the reflected light from said reflex liquidcrystal display device is introduced via said polarized beam splitteragain.
 9. The display apparatus according to claim 8, wherein saidreflex liquid crystal display device and said polarized beam splitterare disposed for each of colors respectively, and the reflected lightbeams from the individual reflex liquid crystal display devices aresynthesized.
 10. The display apparatus according to claim 9, whereinwhite light emitted from a white light source is introduced to adichroic color separation filter via said polarizer/converter, and thelight beams separated therethrough are further separated into lightbeams of individual colors, which are then incident upon said reflexliquid crystal display devices respectively via said polarized beamsplitter, and the reflected light beams are synthesized by means of aprism.
 11. A projection optical system wherein the reflex liquid crystaldisplay device according to any of claims 1 to 5 is disposed in anoptical path thereof.
 12. The projection optical system according toclaim 11, comprising a light source, an optical unit for enablingincidence of the emitted light from the light source onto the reflexliquid crystal display device, said reflex liquid crystal displaydevice, and an optical unit for introducing the reflected light fromsaid reflex liquid crystal display device, wherein all of saidcomponents are disposed in an optical path of said system.
 13. Theprojection optical system according to claim 12, wherein the lightemitted from said light source is incident upon said reflex liquidcrystal display device via a polarizer/converter and a polarized beamsplitter, and the reflected light from said reflex liquid crystaldisplay device is introduced to a projection lens via said polarizedbeam splitter again.
 14. The projection optical system according toclaim 13, wherein said reflex liquid crystal display device and saidpolarized beam splitter are disposed for each of colors respectively,and the reflected light beams from the individual reflex liquid crystaldisplay devices are synthesized and introduced to said projection lens.15. The projection optical system according to claim 14, wherein whitelight emitted from a white light source is introduced to a dichroiccolor separation filter via said polarizer/converter, and the lightbeams separated therethrough are further separated into light beams ofindividual colors, which are then incident upon said reflex liquidcrystal display devices respectively via said polarized beam splitter,and the reflected light beams are synthesized by means of a prism.
 16. Aprojection display system wherein the reflex liquid crystal displaydevice according to any of claims 1 to 5 is disposed in an optical paththereof.
 17. The projection display system according to claim 16,comprising a light source, an optical unit for enabling incidence of theemitted light from the light source onto the reflex liquid crystaldisplay device, said reflex liquid crystal display device, and anoptical unit for introducing the reflected light from said reflex liquidcrystal display device, wherein all of said components are disposed inthe optical path of said system.
 18. The projection display systemaccording to claim 17, wherein the light emitted from said light sourceis incident upon said reflex liquid crystal display device via apolarizer/converter and a polarized beam splitter, and the reflectedlight from said reflex liquid crystal display device is introduced to aprojection lens via said polarized beam splitter again, and further to ascreen.
 19. The projection display system according to claim 18, whereinsaid reflex liquid crystal display device and said polarized beamsplitter are disposed for each of colors respectively, and the reflectedlight beams from the individual reflex liquid crystal display devicesare synthesized and introduced to said projection lens.
 20. Theprojection display system according to claim 19, wherein white lightemitted from a white light source is introduced to a dichroic colorseparation filter via said polarizer/converter, and the light beamsseparated therethrough are further separated into light beams ofindividual colors, which are then incident upon said reflex liquidcrystal display devices respectively via said polarized beam splitter,and the reflected light beams are synthesized by means of a prism.
 21. Aprojection optical system wherein the reflex liquid crystal displaydevice according to any of claims 1 to 5, and an optical unit having anF number under 3, are disposed in an optical path thereof.
 22. Theprojection optical system according to claim 21, comprising a lightsource, an optical unit for enabling incidence of the emitted light fromthe light source onto the reflex liquid crystal display device, saidreflex liquid crystal display device, and an optical unit forintroducing the reflected light from said reflex liquid crystal displaydevice, wherein all of said components are disposed in the optical pathof said system.
 23. The projection optical system according to claim 22,wherein the light emitted from said light source is incident upon saidreflex liquid crystal display device via a polarizer/converter and apolarized beam splitter, and the reflected light from said reflex liquidcrystal display device is introduced to a projection lens via saidpolarized beam splitter again.
 24. The projection optical systemaccording to claim 23, wherein said reflex liquid crystal display deviceand said polarized beam splitter are disposed for each of colorsrespectively, and the reflected light beams from the individual reflexliquid crystal display devices are synthesized and introduced to saidprojection lens.
 25. The projection optical system according to claim24, wherein white light emitted from a white light source is introducedto a dichroic color separation filter via said polarizer/converter, andthe light beams separated therethrough are further separated into lightbeams of individual colors, which are then incident upon said reflexliquid crystal display devices respectively via said polarized beamsplitter, and the reflected light beams are synthesized by means of aprism.
 26. A projection display system wherein the reflex liquid crystaldisplay device according to any of claims 1 to 5, and an optical unithaving an F number under 3, are disposed in an optical path thereof. 27.The projection display system according to claim 26, comprising a lightsource, an optical unit for enabling incidence of the emitted light fromthe light source onto the reflex liquid crystal display device, saidreflex liquid crystal display device, and an optical unit forintroducing the reflected light from said reflex liquid crystal displaydevice, wherein all of said components are disposed in the optical pathof said system.
 28. The projection display system according to claim 27,wherein the light emitted from said light source is incident upon saidreflex liquid crystal display device via a polarizer/converter and apolarized beam splitter, and the reflected light from said reflex liquidcrystal display device is introduced to a projection lens via saidpolarized beam splitter again, and further to a screen.
 29. Theprojection display system according to claim 28, wherein said reflexliquid crystal display device and said polarized beam splitter aredisposed for each of colors respectively, and the reflected light beamsfrom the individual reflex liquid crystal display devices aresynthesized and introduced to said projection lens.
 30. The projectiondisplay system according to claim 29, wherein white light emitted from awhite light source is introduced to a dichroic color separation filtervia said polarizer/converter, and the light beams separated therethroughare further separated into light beams of individual colors, which arethen incident upon said reflex liquid crystal display devicesrespectively via said polarized beam splitter, and the reflected lightbeams are synthesized by means of a prism.